Research on stiffness control of a redundant cable-driven parallel mechanism

Controlling the stiffness of cable-driven parallel mechanisms (CDPM) is of great significance for improving performance in different tasks. A method for stiffness control of a redundant CDPM is presented in this paper. The stiffness matrix of the redundant CDPM is established. On this basis, considering the effect of coupling stiffness, a complete analytical formula for stiffness in different directions is established. Then, the influence of the vector lambda on the stiffness of the CDPM in different directions is analyzed, and a method to control the stiffness of the CDPM through adjusting the vector lambda is proposed. To avoid traversing the value of lambda in the polygon formed by the set of lambda to obtain the appropriate cable tension and keep the cable tension away from the upper and lower limit values, a change path of the vector lambda is designed. When the vector lambda changes along the path, the stiffness of the mechanism can be changed from the minimum value to the maximum value. This method has high computational efficiency and safety. Finally, the correctness and effectiveness of the stiffness control method are verified by experiments. The stiffness control method proposed in this paper can be used to control the stiffness in different directions, and can also be used for different types of redundant CDPMs.